1. Field of the Invention
This invention relates to a headrest support structure, and more particularly to a headrest support structure suitably applied to a headrest supported on an upper end of a seat back.
2. Description of the Related Art
Conventionally, a headrest support structure has headrest stays projecting downward from the headrest, which a inserted into headrest supports fitted in tubular members (square pipes) buried in an upper side portion of a seat back. The headrest support structure is adapted to support the headrest stays while regulating the height of the headrest by height regulating mechanisms in the tubular members. Each of the height regulating mechanisms is formed by providing height regulating engagement portions by forming recesses in a side surface of the relative headrest stay, and providing at an upper end of the relative tubular member with a height regulating locking member retractable with respect to the height regulating engagement portions. Each of the height regulating portions is a recess provided at an upper part thereof with a flat surface perpendicular to the axis of the headrest stay, and at the part of the recess on the lower side of the same flat surface with an inclined surface extending toward an outer circumference of the headrest stay.
The height regulating locking member is given a force in a normal condition toward the headrest stay owing to a resilient member, and can be moved back from the headrest stay by pressing an operating button provided on the tubular member and thereby exerting a rearward force on the height regulating locking member. When the headrest stay in this structure is inserted downward into the relative headrest support, the height regulating locking member is engaged with any one of the plural height regulating engagement portions, and the headrest stay is thereby supported. When the operating button is pressed to disengage the height regulating locking member from the height regulating engagement portion, the user can regulate the height of the headrest to an arbitrary level.
In the headrest stay, an engagement portion formed in a reversely directed state with respect to the other engagement portions is provided below the engagement portion in the lowermost position, by which a slip-off of the headrest can be prevented. This reversely directed engagement portion is a recess provided at a lower part thereof with a flat surface perpendicular to the axis of the relative headrest stay, and at the part of the recess on the upper side of the flat surface with an inclined surface extending toward an outer circumference of the headrest stay. Therefore, when the headrest stay is pulled out upward with the headrest stay inserted in the headrest support, the height regulating locking member engages the flat surface of this engagement portion, and a slip-off of the headrest stay can be prevented.
The above-described conventional headrest support structure has the following problems. That are, the height regulating locking member is given a force in a normal condition toward the headrest stay, so that the headrest stay can be prevented from slipping off. However, this locking member is formed such that the locking member can be moved forward and rearward when the operating button is pressed. Accordingly, when a user presses this operating button, the headrest stay can be pulled out easily from the tubular member. So, the withdrawing of the headrest is attended with danger, and it is inconvenient that the headrest stay is left behind or lost.